Emerging Insights On Negative Pressure Wound Therapy

Negative pressure wound therapy (NPWT) has become an indispensable tool for wound care for many physicians. These authors examine the research on NPWT, evaluate the newest devices on the market and provide guidance for getting reimbursement.

Negative pressure wound therapy (NPWT) has become ubiquitous. In 1993, Fleischmann and colleagues reported the early use of NPWT in open fractures to fill wound defects with a foam dressing attached to a tube and canister applying vacuum suction.1 Since that time, NPWT has revolutionized the practice of wound care and all surgical practices dealing with large tissue defects and associated drainage.

Negative pressure wound therapy was designed to accelerate wound healing via secondary intention by increasing the rate of granulation tissue formation with wound contraction, which expedites the healing process. Indeed, NPWT is valuable in treating acute, sub-acute and chronic wounds of various sizes and depths. This therapy is of utmost importance in diabetic foot ulcers in which fast wound closure is equivalent to limb preservation.

Negative pressure involves an open cell foam or gauze dressing that one applies to the wound base. The dressing is attached to a tube and canister that collects drainage. Negative pressure is indicated in non-ischemic wounds that have no infected or devitalized tissue. After applying a foam or gauze dressing over the wound base, one would apply negative pressure (75-125 mmHg) uniformly over the foam-covered wound base. The foam collapses and forms channels to transport fluid from the wound to the canister. The removal of interstitial fluid from the underlying tissue enables improved capillary circulation with a reduction in interstitial edema, and allows blood flow to the wound as visible on laser Doppler.2

Morykwas and coworkers examined the optimal pressure level in a porcine study that showed the effects of low negative pressure of 25 mmHg and high levels of negative pressure of 500 mmHg in comparison to the standard of 125 mmHg on the rate of granulation tissue formation.3 The study authors concluded that the standard subatmospheric pressure of 125 mmHg had the greatest tissue granulation formation rate.

One would apply suction to the wound in intermittent cycles of five minutes on and two minutes off. A maximum increase in local tissue perfusion occurs with cycling.2 Intermittent therapy causes an increase in cellular proliferation and local growth factors. Chronic non-healing ulcers that arise in diabetic foot wounds have significantly higher levels of matrix metalloproteinases (MMP) in comparison to wounds that are in the process of healing. Enhanced wound healing occurs in both continuous and intermittent cycles by the indirect removal of inhibitory growth factors that occurs with NPWT.4

A Closer Look At The Clinical Evidence Of NPWT

Researchers have observed improved outcomes in diabetic foot ulcers and chronic leg ulcers with the use of NPWT.4 One can also use NPWT concurrently with split thickness skin grafting (STSG) or skin flap techniques as a means for achieving definitive wound closure.

DeFranzo and colleagues have documented the use of NPWT in covering muscle, tendon, bone and hardware in the lower extremity, showing great success.5 Studies also show advantageous effects in the treatment of complex diabetic foot ulcers through faster healing rates, increased proportions of healed wounds and a decrease in the rate of re-amputation.6 In a multicenter, randomized controlled trial involving 342 patients, Blume and coworkers demonstrated that patients treated with NPWT had a greater proportion of healed diabetic foot ulcers and significantly fewer secondary amputations than patients treated with advanced moist wound therapy.7

Negative pressure wound therapy is versatile as it assists granulation tissue formation and consequently prepares the wound bed for STSG placement. A granular wound bed is well vascularized and enables an optimal setting for skin grafting. When applying a STSG, place the foam over a non-adherent dressing covering the skin graft. After applying the negative pressure, the foam conforms to the wound base evenly with the skin graft. This increases graft take by improving skin graft adherence to the underlying wound base. The constant removal of fluid and exudates prevents seroma or hematoma formation.

Additionally, NPWT acts as a bolster dressing and prevents shear forces. Blume and coworkers analyzed the use of NPWT versus a conventional cotton bolster dressing with STSG in reconstructive surgery of the foot and ankle.8 The authors found improved graft survival and less incidence of repeat skin grafting due to complications and failures in comparison to conventional cotton dressings.8,9 With skin grafts, one should leave the NPWT device in place for a range of five to seven days, the time it takes for the skin graft to vascularize.

The principles of using NPWT over an incision are similar in that NPWT keeps the wound edges well coapted during therapy. In the orthopedic trauma literature, Gomoll and coworkers showed the benefits of using NPWT over an incision to reduce postoperative swelling and management of drainage.10 Less frequent dressing changes are required in a closed surgical wound, which may potentially reduce the rate of infection.

The role of decreasing bacterial colonization is debatable with NPWT. Early studies revealed a decrease in bacterial loads in animal models.2 However, subsequent studies evaluating deep tissue specimens show otherwise. There is evidence suggesting that NPWT does not significantly decrease bacterial load but rather changes the bacterial morphology of the wound from non-fermenting gram-negative rods to colonization of Staphylococcus aureus.11 In another study of serial wound cultures, Weed and colleagues found evidence of increased bacterial colonization.12 These outcomes highlight the need for careful wound surveillance, especially in diabetic foot ulcers.

The benefits of NPWT not only include accelerated wound healing but also increased patient comfort by decreasing pain. Since patients can leave the NPWT device in place for several days, it does not require daily dressing changes as one sees with “wet-to-dry” dressings. Some patients may experience dressing change pain. However, one can mitigate this by injecting lidocaine solution into the foam dressing itself, allowing the lidocaine to soak the wound bed for a few minutes.

Although NPWT dressing changes have traditionally occurred three times a week (i.e. Monday/Wednesday/Friday), we have found that twice-a-week dressing changes (i.e. Monday/Thursday or Tuesday/Friday) may be as effective while alleviating the pain and the logistical cost to our patients. Pain and quality of life measurements are superior in patients with lower extremity leg ulcers who have undergone NPWT in comparison to conventional therapy as they are on less bed rest and are able to ambulate earlier with NPWT.15

Assessing The Benefits Of Different NPWT Devices

Now that there are multiple NPWT devices on the U.S. market, our options have expanded greatly and include different types of dressing interfaces (polyurethane foam vs. gauze), battery-powered vs. mechanically-powered suction, and small disposable devices versus larger rental devices.

The debate over the effectiveness of improved granulation tissue formation between foam and gauze has so far occurred with porcine models. Studies have evaluated wound contraction and microvascular blood flow within the tissue and showed similar results when comparing foam and gauze.2,13 In biopsies of the wound bed, there is evidence of tissue pulling through foam and gauze space, signaling granulation tissue formation and reduction in wound surface area with the two separate dressing interfaces.14 In our institution, we prefer polyurethane foam dressing as gauze dressings may disintegrate faster and the gauze fragments may be embedded within the wound bed.

The introduction of simple, smaller, portable devices on the market has now enabled the care of wounds via NPWT on an outpatient basis at home or in a skilled nursing facility. This ultimately reduces the length of hospitalization with a decrease in overall medical cost and simplifies delivery and care logistics.16

SNaP (Spiracur) is a small NPWT device that is lightweight (2.2 oz) and mechanically powered (“non-powered”) in comparison to the widely-used ActiVac Therapy System (KCI), which is electrical with a rechargeable battery. SNaP functions with metal springs that generate continuous negative pressure therapy and is designed to be single-use and disposable as the canister for the wound fluid is integrated within the device.

A multicenter, comparative, randomized control trial evaluated SNaP and VAC therapy in healing lower extremity wounds and showed comparable results in patients treated for diabetic foot ulcers and venous ulcers.17 In our clinical experience, the clinical efficacy of NPWT has been equivalent for both devices as long as the pressure settings and the dressing interface are the same.

The smaller design of the SNaP has a distinct advantage in that one may apply the small form and light weight for most wound care patients, including older, frail patients, who may find traditional battery-operated devices to be heavy. The aforementioned randomized controlled study found that the SNaP system interferes significantly less with overall activity, sleep and social interaction than the VAC therapy system.17 On the other hand, because of its small canister capacity, the SNaP device may not be suitable in cases that require a large amount of wound drainage, for example, for the treatment of large venous leg ulcers.

A Pertinent Overview On Clinical Uses Of NPWT

Negative pressure wound therapy is an adjunctive therapy to improve wound healing in the field of surgery and wound care. As with any other wound dressing, it is imperative to make sure the wound is free of ischemia and infection before the application of NPWT dressings.

In our institution, we use a laser Doppler machine (SensiLase, Vasamed) to measure skin perfusion pressure (SPP) and pulse volume recordings (PVRs) to rule out ischemia in lower extremities. In grossly infected wounds, purulence clogs the open pores of NPWT foam dressings. Physicians should not use NPWT in such patients until they can debride and decontaminate the wound sufficiently in the operating room along with appropriate administration of antibiotics.

Delayed closure and increased granulation tissue formation. This is the original indication for NPWT, which promotes healthy granulation tissue over the wound bed faster than conventional wound dressings.3 Negative pressure also facilitates granulation tissue formation over tendon, fascia, bone or otherwise hard-to-heal wounds (i.e. previously operated or irradiated tissues). In the operating room, we routinely drill holes in fascia and bones to create microbleeding in order to promote granulation tissue formation. Surgeons may allow the wound to heal via secondary intention or one may opt for delayed primary closure and the use of NPWT.

Status-post skin graft. This is a newer indication but clinicians routinely use NPWT for this in the hospital setting. It is known that hematoma and seroma formation under the skin graft are the primary causes of graft failure. After the application of the skin graft, cover the graft with non-adherent mesh (i.e. Vaseline gauze or plastic contact layer) and then apply NPWT directly over the graft. This treatment allows effective drainage of wound fluids while bolstering the grafts against the wound bed.

Conventionally, we prefer to keep NPWT dressings on wounds over a five- to seven-day period in order to minimize the graft disturbance. In addition, some clinicians advocate lowering the suction pressure to 75 or 100 mmHg to minimize the graft disturbance. However, in our experience over the years, we have found that the 125 mmHg setting may work just as effectively.

Surgical incisions and status-post skin flap. As with skin grafting, clinicians may apply NPWT to any skin flap as well as surgical incisions, assuming that the incision is also protected with a non-adherent mesh dressing. This application is most useful in complex incisions or skin flaps, which benefit from increased blood flow to the skin edges, or if there is a significant “dead space” underneath the flaps that one should fill with granulation tissue. We also prefer to leave the dressing on for five to seven days, although a longer duration may cause the maceration of the skin edges. We recommend placing the sutures farther apart than conventional primary closure to promote drainage. There are currently a few disposable NPWT devices, such as Prevena (KCI) or PICO (Smith and Nephew) that are specifically designed for large surgical incisions. Another relatively new option is the ciSNaP system (Spiracur), which minimizes tension on staples and sutures, and helps reduce the risks of dehiscence and infection.

Continuous or intermittent irrigation of chronic wounds. Although there are no randomized control trials showing efficacy in wound healing with NPWT and topical wound solution instillation devices (which provide irrigation and decontamination), various case reports have shown anecdotal support for such approaches.18 It has been proposed that instilling a topical antimicrobial solution (i.e, Dakin’s solution) intermittently may help in reducing biofilm in heavily contaminated chronic wounds. VAC Ulta (KCI) allows programmable instillation of irrigation fluid and one may use it for this purpose.

What You Should Know About Reimbursement And NPWT

The application of NPWT dressings and educating your patients about these dressings takes time and expertise, for which you may be reimbursed. Here are some explanations of the relevant codes.

This CPT code was introduced in 2005. It allows the clinicians to bill for the time, technical knowledge and the expertise to apply a “powered” NPWT device, such as VAC therapy. Clinicians may use this code in the office as it does not apply to OR applications of NPWT. For the total wound surface area over 50 cm2, use CPT 97606 in place of CPT 97605 (Work RVU 0.6, Non-facility RVU 0.63).

G0456 (HCPCS code)Descriptor: Negative pressure wound therapy, using a disposable mechanically powered device, including topical application, wound assessment and instructions for ongoing care, per session. Total wound surface area less than or equal to 50 cm2. For the wound size over 50 cm2, G0457 should be used.

Introduced in 2013, this G code (G0456) is a new Healthcare Common Procedure Coding System (HCPCS) code for billing Medicare for supplies and material, specific to the use of the SNaP system. This G code (G0456) represents both product and service components combined into one therapy code. It is a “significant procedure” and multiple procedure reduction applies. Physicians, facilities or both may bill this code based upon the types of service being administered as well as the care site in which one delivers care.

As this article goes to press, the product side of the code has already been assigned to a payment rate in the Outpatient Prospective Payment System fee schedule (the hospital outpatient Ambulatory Payment Classification value) as $209.65 and the physician’s service component (RVUs) in the outpatient hospital facility is “to be determined” by the local medical carrier upon review of documentation. Currently, there are no National Correct Coding Initiative edits established by CMS to determine what one can or cannot bill simultaneously. The physician would determine this on a case-by-case basis upon claim submission.19

In Conclusion

Negative pressure wound therapy is a safe, versatile and clinically proven modality, which reduces wound closure time, and has recently enjoyed new portability and irrigation functionality with the introduction of the SNaP and VAC Ulta devices. The increased use of NPWT will overall reduce medical care costs and provide better patient outcomes in the care of diabetic foot ulcers.

Dr. Shum is a third-year resident with the Cedars Sinai Medical Center Podiatric Medicine and Surgery Residency Program in Los Angeles.

Dr. Suzuki is the Medical Director of the Tower Wound Care Center at the Cedars-Sinai Medical Towers. He is also on the medical staff of the Cedars-Sinai Medical Center in Los Angeles and is a Visiting Professor at the Tokyo Medical and Dental University in Tokyo. He can be reached via email at Kazu.Suzuki@CSHS.org .

Editor’s note: For further reading, see “A Guide To Current And Emerging NPWT Modalities” in the July 2012 issue of Podiatry Today or “Expert Pointers On Negative Pressure Wound Therapy” in the July 2007 issue.